Precision Glycopolymer Bacteriochlorin Conjugates for Probing HA-CD44 Interactions Project Summary/Abstract One of the major challenges in studying carbohydrate-protein interactions is the low binding affinity of individual carbohydrate subunits. Molecular scaffolds that mimic glycoconjugates can be useful for studying these processes. However, the lack of reliable and reproducible methods for the preparation of precise, well- defined molecular scaffolds has so far limited the development of these compounds. Our proposed fundamental research aims to overcome these limitations through the modular synthesis and evaluation of a series of well-defined, tunable bacteriochlorin conjugates that can be used to systematically probe carbohydrate-protein interactions. The primary goal of our research is to synthesize oligoproline scaffolds bearing bacteriochlorins and differentially-functionalized hyaluronic acid (HA) disaccharides. These so-called hyaluronic acid bacteriochlorin-based oligoproline conjugates (HABOCs) will be used to study how HA presentation impacts its recognition by glycoprotein CD44. We chose to study this interaction between HA and CD44 because of its importance in human health and diseases, including tumor metastasis. The HA-CD44 interaction is responsible for both pro- and anti-inflammatory properties, can promote or inhibit cell migration, and can activate or stop cell division and differentiation. Interestingly, these seemingly disparate roles have been shown to be regulated by factors that involve specific cell types as well as the location and size (native high molecular weight (HMW) vs lower molecular weight oligosaccharides (oHA)) of HA. What is lesser known is whether HA presentation impacts HA-CD44 binding. Our research aims to answer this question. The second goal of our studies is to determine whether we can exploit the HABOC interaction to develop cell penetrating phototheranostics that use CD44 receptor-mediated endocytosis. The bacteriochlorin, which absorbs in the NIR between 700-800nm, shows significant promise as a next generation theranostic for image-guided and photodynamic therapies. We hypothesize that HABOCs can be designed to precisely present HA to mimic HMW-HA and o-HA binding, that these HABOCs will interact differently with cells expressing different levels of CD44, and that our HABOCs can be used to quantify cell uptake and inactivation via photodynamic therapy (PDT). With the aforementioned hypotheses in mind, our specific aims are: (i) To synthesize a series of well- defined, hyaluronic acid bacteriochlorin-based oligoproline conjugates (HABOCs), (ii) To evaluate HABOC- CD44 interactions using isothermal titration calorimetry (ITC) and saturation transfer difference (STD) NMR, and (iii) To conduct cellular uptake and phototoxicity studies to determine whether HABOCs interact with cell lines expressing different levels of CD44 and whether this interaction can be used to inactivate cells using PDT. Our research addresses the questions: How does HA length and presentation impact the HA-CD44 interaction? and Can we use HABOCs to selectively target cells with different levels of CD44 expression?